(i) Field of the Invention
The present invention relates to a technical field of a display position control apparatus and, more particularly, to a technical field of a display position control apparatus for controlling a display position of an image in a matrix type display apparatus.
(ii) Description of the Related Art
When an image is displayed using a matrix type display apparatus such as a liquid crystal display or a PDP (Plasma Display Panel), generally, the display position of the image in the display apparatus is controlled on the basis of a vertical sync signal and a horizontal sync signal included in an image signal that corresponds to the image to be displayed and is inputted from the outside.
In this instance, as a relation between the vertical sync signal, the horizontal sync signal, and the image signal as the image itself, various forms are currently used. There is a display position control method in which the vertical sync signal and the horizontal sync signal are supplied independent of each other and the signals are also inputted from the outside independent of the image signal, namely, the method using separate type sync signals as one of the above various forms.
In this case, when the display position of the image is controlled using the separate type sync signals, in order to perform the position control in the horizontal direction, the display position in the horizontal direction is first determined on the basis of timing of the horizontal sync signal as a reference. In order to perform the position control in the vertical direction, the vertical sync signal is latched using the horizontal sync signal to count the number of horizontal sync signals on the basis of timing of the vertical sync signal. Consequently, the display position in the vertical direction is determined.
In this case, when the number of horizontal sync signals counted at an interval between the adjacent vertical sync signals on a time axis (namely, the number of horizontal scan lines counted at an interval between the adjacent vertical sync signals) is constant while one image is displayed, the necessary image can be displayed with high image quality without being fluctuated in the vertical direction (namely, being overlapped so as to be blurred in the vertical direction). In this instance, in order to maintain the predetermined number of horizontal sync signals counted at an interval between the adjacent vertical sync signals while one image is displayed as mentioned above, it is necessary to prevent the vertical sync signal and the horizontal sync signal from being inputted overlappingly on the time axis or being inputted at timings extremely close to each other, namely, prevent phase distortion between the vertical sync signal and the horizontal sync signal (hereinbelow, the state in which the phase distortion is caused is referred to as a phase mismatch state).
However, the above conventional display position control method using the separate type sync signals has the following disadvantages. That is, a device for generating and outputting the vertical sync signal and the horizontal sync signal has a variation in delay time, a processing of determining the relation between the phase of the vertical sync signal and that of the horizontal sync signal is not performed in the device, and the above-mentioned phase mismatch state is actually caused by various noises mixed in a step of generating and transmitting the vertical sync signal and the horizontal sync signal. Consequently, the image is displayed overlappingly, particularly, in the vertical direction in the display apparatus.